1. Department of Microbiology, University of Manitoba, Winnipeg, MB, R3T 2N2 Canada, Freshwater Institute, Department of Fisheries and Oceans, 501 University Crescent, Winnipeg, MB, R3T 2N6 Canada, and Department of Biochemistry and Microbiology, Cook College, Rutgers University, New Brunswick, New Jersey 08901-8525